Many people have complained that GURPS is too generic. That the GM and players have to work to breath life into a campaign. This wonderful little book addresses that issue quite nicely. The author has created 67 detailed nasty critters; their characteristics, their goals, their methods, and their environments. Then he provides 2-3 "adventure seeds" for each monster that the GM can flesh out quickly and easily to create adventures of varying degrees of complexity and challenge. These "adventure seeds" are extremely well done and GMs might want to buy the book just for all the adventuring ideas put forth there.
The creatures span all manner of time and space and could be used in a science fiction, fantasy, historical, or even a super-hero campaign with little effort.
My only complaint is that there's no way to index the creatures power against the strength of the party. It might well take some experience and possibly some GM intervention to avoid accidentally killing the party. There is an index in the back that provides a thumbnail sketch of all the critters but some sort of power rating would have made the book perfect instead of extremely good.
The descriptions are wonderfully macabre and the artwork does a great job of further setting the tone. There's no question that the author really enjoyed creating this book. There's still some lingering questions about the type of personality that would come up with some of these monsters, but that's not your problem. Just go out and buy the book and enjoy how it pumps up your campaign without any extra effort on your part.